Nonreducible dielectric ceramic composition

ABSTRACT

Disclosed is a nonreducible dielectric composition. Provided is a highly reliable TC based dielectric composition prepared by adding a sintering additive having excellent qualities to a conventional (Ca 1-x Sr x ) m (Zr 1-y Ti y )O 3  based dielectric composition, so that it can be sintered under a reducing atmosphere to be used in formation of a nickel electrode, can be sintered at a temperature of less than 1,300° C., and even more, at a low temperature of 1,250° C., and has a small dielectric loss and a high resistivity. The composition of the present invention includes a nonreducible dielectric composition comprising a main component expressed by the general formula, (Ca 1-x Sr x ) m (Zr 1-y Ti y )O 3 , which has the ranges of 0≦x≦1, 0≦y&lt;0.09, and 0.7≦m≦1.05; and 0.5-10 wt % of a minor component expressed by the general formula, aMnO-bSiO 2 -dR 1 O-eR 2 O 2  (a+b+d+e=100, R 1  is at least one element selected from the group consisting of Mg, Ca, Sr and Ba, and R 2  is at least one element of Zr and Ti), which has the ranges of 20≦a≦60, 10≦b≦65, and 0&lt;(d+e)≦65.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a nonreducible dielectric compositionto be applied to a laminated ceramic capacitor for temperaturecompensation, and the like, and more particularly, to a nonreducibledielectric composition having a high insulation resistance and a smalldielectric loss, which can be sintered under a reducing atmosphere usingan internal electrode containing nickel (Ni).

2. Description of the Related Art

Demand for laminated ceramic capacitors is increasing yearly due todigitalization, miniaturization and high-functionalization of electronicproducts, and they have been used in a variety of electronic devicessuch as televisions, computers, video cameras, cellular phones and thelike. In recent years, there has been an increased need for a laminatedceramic capacitor having excellent characteristics, that is, a highinsulation resistance, a small dielectric loss, and a reduced variationin capacitance upon a variation in temperature.

A conventional laminated ceramic capacitor was manufactured by sinteringa high-priced noble metal such as palladium (Pd) or silver-palladium(Ag—Pd) alloy including palladium as an internal electrode, and aBaO—Nd₂O₃—TiO₂— or MgTiO₃—CaTiO₃—based dielectric composition under anatmosphere of 1,100-1,350° C. However, there have been problems in thatdue to oxygen vacancies formed when sintered under a reducingatmosphere, the composition exhibits a lowered insulation resistance anda degraded reliability, and thus Ni cannot be employed as an internalelectrode.

In order to use nickel as an internal electrode, such a composition mustbe able to be sintered under a reducing atmosphere. Known up until nowhas been a CSZT based composition disclosed in Japanese Patent Laid-OpenPublication No. 10-335169. The composition consists of a main componentexpressed by the general formula,(Ca_(1-x)Sr_(x))_(m)(Zr_(1-y)Ti_(y))O₃, which meets the conditions:0≦x≦1, 0≦y≦0.1 and 0.75≦m≦1.04; and a minor component of BCG: 0.5-15 mol%, MnO: 0.2-5 mol %, Al₂O₃: 0.1-10 mol % (on the basis of the totalmoles of the main component) and a rare earth element.

The composition disclosed in the above publication has advantages ofnonreducibiliy and a reduced variation in capacitance upon a variationin temperature. Furthermore, the composition overcomes a largedielectric loss at high temperature-low frequency condition encounteredin lithium glass (Li-glass) based composition. Also, the composition ischaracterized in that uniform and small grain size can be obtained.

In spite of these advantages, in the above composition, the sinteringtemperature of dielectric is as high as 1,300° C., and the sinteringinitiating temperature of dielectric is higher than that of Ni used foran internal electrode. As a result, there is a problem in that cracks,defects or the like are caused by mismatching between the internalelectrode and ceramic. This is because the metal of the electrodeexhibits a shrinkage rate higher than that of ceramic during thesintering process.

Meanwhile, Japanese Patent Laid-Open Publication No. 63-289709 disclosesa composition consisting of a main component,(Ca_(x)Sr_(1-x))_(m)(Zr_(y)Ti_(1-y))O₃ (0.3≦x≦0.5, 0.92≦y≦0.98, and0.95≦m≦1.08) and a minor component, MnO₂(0.01-4.0 wt %) and SiO₂(2.0-8.0wt %), the composition being sinterable under a reducing atmosphere. Thedielectric constant of Ca/Sr in the composition is relatively high,below 1.

Nevertheless, the above composition still has a problem in that adielectric loss at high temperature—low frequency condition is large.Furthermore, the composition involves generation of defects bymismatching between electrode metal and ceramic during a sinteringprocess, because sintering temperature of ceramic is high, up to 1,300°C.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made in view of the aboveproblems, and it is an object of the present invention to provide ahighly reliable dielectric composition prepared by adding a sinteringadditives having excellent qualities to a conventional(Ca_(1-x)Sr_(x))_(m)(Zr_(1-y)Ti_(y))O₃ based dielectric composition, sothat it can be sintered under a reducing atmosphere to be used information of a nickel electrode, can be sintered at a temperature ofless than 1,300° C., and even more, at a low temperature of 1,250° C.,and has a small dielectric loss and a high resistivity.

Another abject of the present invention is to provide a dielectriccomposition meeting COG/CH characteristics in accordance with the EIA(Electric Industry Association) Standard.

In accordance with one aspect of the present invention, there isprovided a nonreducible dielectric composition comprising a maincomponent expressed by the general formula,(Ca_(1-x)Sr_(x))_(m)(Zr_(1-y)Ti_(y))O₃, which has the ranges of 0≦x≦1,0≦y<0.09, and 0.7≦m≦1.05; and 0.5-10 wt % of a minor component expressedby the general formula, aMnO-bSiO₂-cAl₂O₃ (a+b+c=100), which has theranges of 20≦a≦60, 10≦b≦65, and 1≦c≦10.

In accordance with another aspect of the present invention, there isprovided a nonreducible dielectric composition comprising a maincomponent expressed by the general formula,(Ca_(1-x)Sr_(x))_(m)(Zr_(1-y)Ti_(y))O₃, which has the ranges of 0≦x≦1,0≦y≦0.09, and 0.7≦m≦1.05; and 0.5-10 wt % of a minor component expressedby the general formula, bSiO₂-cAl₂O₃-dR₁O (b+c+d=100, R₁ is at least oneelement selected from the group consisting of Mg, Ca, Sr and Ba), whichhas the ranges of 10≦b≦65, 0≦c≦10 and 0≦d≦50.

In accordance with still another aspect of the present invention, thereis provided a nonreducible dielectric composition comprising a maincomponent expressed by the general formula,(Ca_(1-x)Sr_(x))_(m)(Zr_(1-y)Ti_(y))O₃, which has the ranges of 0≦x≦1,0≦y<0.09, and 0.7≦m≦1.05; and 0.5-10 wt % of a minor component expressedby the general formula, aMnO-bSiO₂-dR₁O-eR₂O₂ (a+b+d+e=100, R₁ is one ortwo elements of Mg, Ca, Sr and Ba, and R₂ is at least one of Zr and Ti),which has the ranges of 20≦a≦60, 10≦b≦65, and 0<(d+e)≦65.

Finally, in accordance with yet another aspect of the present invention,there is provided a nonreducible dielectric composition comprising amain component expressed by the general formula,(Ca_(1-x)Sr_(x))_(m)(Zr_(1-y)Ti_(y))O₃ which has the ranges of 0≦x≦1,0≦y<0.09, and 0.7≦m≦1.05; and 0.5-10 wt % of a minor component expressedby the general formula, bSiO₂-dR₁O-eR₂O₂ (b+d+e=100, R₁ is at least oneelement selected from the group consisting of Mg, Ca, Sr and Ba, and R₂is one of Zr and Ti), which has the ranges of 10≦b≦65, 10≦d≦20, and10≦e≦60.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the nonreducible dielectric composition in accordance withthe present invention will be described in detail.

The present invention relates to a nonreducible dielectric compositionin which its main component is expressed by the general formula,(Ca_(1-x)Sr_(x))_(m)(Zr_(1-y)Ti_(y))O₃. In accordance with the presentinvention, it is required that x, y and m meet the conditions of 0≦x≦1,0≦y<0.09, and 0.7≦m≦1.05, using conventionally available materials.

The subscript x in the main component is within the range of 0≦x≦1. Thatis, the composition may contain any mixture of Ca and Sr, or only oneelement of both of them. The higher the value of x, i.e., the higher theproportion of Sr, the larger the mean grain size of crystals becomes andthe more the dielectric constant increases. In order to obtain a smallersintered grain size, preferred range of x is less than 0.5.

The subscript y in the main component is within the range of 0≦y<0.09. Atemperature coefficient of capacitance and a dielectric constant dependon the y value. The higher the value of y, the more negative thetemperature coefficient of capacitance becomes and the more thedielectric constant increases. In order to obtain a COG/CH baseddielectric composition in accordance with the present invention, thecomposition range of y is limited to less than 0.09. As a result, acomposition can be obtained that meets the requirement of −30˜+30 ppm/°C. for a temperature coefficient of capacitance as COG characteristicsused for capacitor for thermal compensation or the requirement of−60˜+60 ppm/° C. for a temperature coefficient of capacitance as CHcharacteristics used for capacitor for thermal compensation.

The subscript m of the main component is within the range of 0.7≦m≦1.05.Undesirably, however, if m is less than 0.7, the dielectric lossincreases, and if m exceeds 1.05, sintering temperature rises.

A minor component is also included in the dielectric composition ofpresent invention. The minor component is added as a sintering additiveselected from sintering additives of four types. In accordance with thepresent invention, the added amount of sintering additive is preferably0.5-10 wt % based on the total amount of the main component. Where theamount of the sintering additive is less than 0.5 wt %, sinteringproperty becomes poor. Where the amount exceeds 10 wt %, intrinsicqualities of dielectric become poor, for example, a low dielectricconstant, an increased dielectric loss, etc.

The first type sintering additive is a minor component expressed by thegeneral formula, aMnO₂-bSiO₂-cAl₂O₃ (a+b+c=100), which has the ranges of20≦a≦60, 10≦b≦65, and 0<c≦10.

The MnO₂ serves as an acceptor and thus absorbs free electrons in oxygenvacancies made when the additive is sintered under a reducingatmosphere, which in turn make it possible to improve nonreducibility.Undesirably, however, if the MnO₂ content is less than 20 mol %, thevalue of resistivity becomes lower, and if the MnO₂ content exceeds 60mol %, solid solution is not good enough for the MnO₂ to be deposited,and sintering property becomes poor.

Content of SiO₂ is defined as 10-65 mol %. If the content is less than10 mol %, it has no effect, and if the content exceeds 65 mol %,sintering property is prone to worsen due to viscosity.

The Al₂O₃ is added to improve water resistance and mechanical strength.Since Al₂O₃ is deposited without being dissolved when added in excess,it is preferable for Al₂O₃ to be contained in an amount of less than 10mol % in the minor component.

The second type sintering additive is a minor component expressed by thegeneral formula, bSiO₂-cAl₂O₃-dR₁O (b+c+d=100, R₁ is at least oneelement chosen from Mg, Ca, Sr and Ba), which has the ranges of 10≦b≦65,0<c≦10 and 0≦d≦50.

The third type sintering additive is a minor component expressed by thegeneral formula, aMnO-bSiO₂-dR₁O-eR₂O₂ (a+b+d+e=100, R₁ is at least oneelement of Mg, Ca, Sr and Ba, and R₂ is at least one element chosen fromZr and Ti), which has the ranges of 20≦a≦60, 10≦b≦65, 0<(d+e)≦65.

Finally, the fourth type sintering additive proposed in the presentinvention is a minor component expressed by the general formula,bSiO₂-dR₁O-eR₂O₂ (b+d+e=100, R₁ is at least one element selected fromthe group consisting of Mg, Ca, Sr and Ba, and R₂ is one of element Zrand Ti), which has ranges of 10≦b≦65, 10≦d≦20 and 10≦e≦60.

Metal oxides expressed as R₁O or R₂O₂ may be contained as a part of theminor component to improve properties of the minor component itself suchas water resistance, acid resistance, etc. As a metal ion to be used forthis purpose, R₁ is a least one element selected from the groupconsisting of Ba, Ca, Sr and Mg, and R₂ is a least one element of Ti andZr. These metal oxides modify the surfaces of glasses or bind tonon-bridging oxygen ions, thereby making it possible to improve chemicalstability of the minor component. These metal oxides are added to theextent that the sintering property is not lowered and their effects areaccomplished, without departing from the ranges of the minor componenthaving a composition of the above sintering additives.

EXAMPLE

Hereinafter, the present invention will be illustrated in detail by wayof the non-limiting examples.

In order to prepare (Ca_(1-x)Sr_(x))_(m)(Zr_(1-y)Ti_(y))O₃ basednonreducible dielectric composition in the proportions shown in table 1below, CaCO₃, SrCO₃, TiO₂ and ZrO₂ were weighed, and the weighedmaterials were mixed, then sintered at a temperature of 1,100-1,250° C.for several hours and then pulverized to form a main component.

As for a minor component, MnO₂, SiO₂, CaCO₃, MgCO₃, SrCO₃, BaCO₃, Al₂O₃,ZrO₂ and TiO₂ were weighed in the proportions shown in table 2 below,mixed, completely dissolved in a platinum crucible at 1,500° C. andquenched quickly to room temperature to form the component as a glassphase, or alternatively, weighed, mixed, sintered at a temperature of1,200° C. for several hours, and then pulverized to form the component.

The main component and the minor component were weighed in theproportions shown table 1, PVB or acrylic binder or solvent,plasticizer, etc. were added thereto, and then dispersed with ahigh-energy mill to form a slurry, which was then transformed into asheet with a thickness of 10 μm.

An electrode paste using a nickel or a nickel-contained non-metalelectrode material as an internal electrode was printed on thetransformed sheet and then laminated. The resultant laminate was cut toform green chips, the green chips were baked out in air at 200-300° C.for 12-48 hours, then in nitrogen (N₂) atmosphere at 200-600° C. for0.5-48 hours.

After completion of the baking-out, for avoiding oxydation of aninternal electrode, the green chips were sintered under a reducingatmosphere (a partial pressure of oxygen 10⁻⁸—10⁻¹⁵ atm) at a sinteringtemperature of 1,250° C. or below, and then heated under 10⁻⁵—10⁻⁸ atmof a partial pressure of oxygen in a temperature range of 1,100-800° C.to obtain a sintered body.

The sintered body thus obtained was subjected to polishing.Subsequently, an external electrode was formed of a metal such as Cu.The external electrode was sintered at approximately 700-900° C. andthen was plated for avoiding oxydation and soldering.

TABLE 1 Glass frit Added Amount Specimen X 1-x Y 1-y m (GF) Type of GFExam. 1 1.0 0.0 0.0 1.0 1.0 A 3.0 Exam. 2 1.0 0.0 0.0 1.0 1.0 B 3.0Exam. 3 1.0 0.0 0.0 1.0 1.0 C 3.0 Exam. 4 1.0 0.0 0.0 1.0 1.0 D 3.0Exam. 5 1.0 0.0 0.0 1.0 1.0 E 3.0 Exam. 6 1.0 0.0 0.0 1.0 1.0 F 3.0Exam. 7 1.0 0.0 0.0 1.0 1.0 H 3.0 Exam. 8 1.0 0.0 0.0 1.0 1.0 I 3.0Exam. 9 0.0 1.0 0.04 0.96 1.0 H 2.5 Exam. 10 0.7 0.3 0.03 0.97 1.0 A 2.5Exam. 11 0.7 0.3 0.03 0.97 1.0 C 2.5 Exam. 12 0.7 0.3 0.03 0.97 1.0 F2.5 Exam. 13 0.7 0.3 0.03 0.97 1.0 H 2.5 Exam. 14 0.7 0.3 0.03 0.97 1.0I 2.5 Exam. 15 0.7 0.3 0.03 0.97 1.0 H 2.5 Exam. 16 0.7 0.3 0.04 0.961.0 H 2.5 Comparative 1.0 0.0 0.0 1.0 1.0 G 3.0 Exam. 1 Comparative 0.01.0 0.0 1.0 1.0 B 2.5 Exam. 2 Comparative 0.7 0.3 0.03 0.97 1.0 G 2.5Exam. 3 Comparative 0.7 0.3 0.09 0.91 1.0 H 2.5 Exam. 4

TABLE 2 R₁ R₂ Specimen MnO₂ SiO₂ Al₂O₃ BaO MgO CaO SrO TiO₂ ZrO₂ A 35.0256.20 8.78 B 50.00 38.85 11.15 C 50.00 8.29 8.43 33.27 D 22.22 18.5218.52 40.74 E 63.12 18.44 18.45 F 29.13 49.74 6.86 3.45 10.82  G* 50.0025.00 25.00 H 55.24 40.19 4.57 I 42.73 9.02 18.92 29.33 Specimenindicated with an asterisk (*) is that having a sintering additivecondition out of the present invention.

As mentioned above, each specimen prepared in the compositionproportions shown in table 1 and table 2, respectively, was tested tomeasure its characteristics.

The evaluated items were a dielectric constant, a temperaturecoefficient of capacitance, tan δ and resistivity, which were practicedas the following manner. The dielectric constant was measured on thebasis of capacitance at 1 MHz, 25° C., 1 Vrms(AC voltage:1V) and tanδwas also measured at 1 MHz, 25° C., 1 Vrms, which indicates dielectricloss. The temperature coefficient of capacitance (TCC) was determinedover −55° C./125° C. on the basis of capacitance at 25° C. and was givenby the equation:TCC(ppm/° C.)=[(C _(T) −C _(25°) C.)/C _(25° C.)]/(T−25° C.) ★10^(6,)

where −55° C.≦T≦+125° C.

The resistivity was measured inΩ cm unit at 25° C., after applying arated voltage of 50V for 60 seconds. The results for each specimen areshown in table 3 below.

TABLE 3 TCC (ppm/° C.) Grain Sintering Dielectric Tanδ Character-Resistivity size Specimen Temp. (° C.) Constant (%) 125° C. −55° C.istic (Ω cm) (μm) Exam. 1 1,250 27.59 0.04 39.6 40.3 CH >E15 1.6 Exam. 21,250 28.98 0.02 −12.2 −23.5 COG >E15 2.0 Exam. 3 1,300 28.59 0.03 −3.0−8.8 COG >E15 1.4 Exam. 4 1,250 28.50 0.03 −12.1 −22.3 COG >E15 1.8Exam. 5 1,300 26 0.05 −18.5 −37.3 CH >E15 1.6 Exam. 6 1,230 28.37 0.0325.6 20.8 COG >E15 1.5 Exam. 7 1,200 27.88 0.03 42.9 41.5 CH >E15 1.3Exam. 8 1,250 28.66 0.03 1.7 −1.1 COG >E15 1.5 Exam. 9 1,250 33.33 0.0522 −25 COG >E15 1.5 Exam. 10 1,230 31.39 0.04 23.5 27.5 COG >E15 1.3Exam. 11 1,300 31.74 0.04 4.8 −13.3 COG >E15 1.4 Exam. 12 1,200 32.010.04 7.1 4.0 COG >E15 1.5 Exam. 13 1,200 33.13 0.04 35.6 20.1 CH >E151.3 Exam. 14 1,300 31.73 0.04 2.9 −10.3 COG >E15 1.3 Exam. 15 1,200 32.10.03 35 27 CH >E15 1.3 Exam. 16 1,200 33.4 0.03 −9.2 −9.6 COG >E15 1.3Comp. 1,300 21.25 0.06 12.3 10.9 COG >E15 0.7 Exam. 1 Comp. 1,300 30.140.05 134 162 — >E15 2.5 Exam. 2 Comp. 1,230 35.81 0.04 −33.6 −85.3— >E15 1.4 Exam. 3 Comp. 1,200 38.4 0.04 −147 −180 PH >E15 1.5 Exam. 4

As can be seen from the above table 3, examples of the present inventionhad a small dielectric loss(tan δ) and a high resistivity, could besintered under a reducing atmosphere to be used in formation of a nickelelectrode and could be sintered at temperature of less than 1,300° C.,and even more, at a low temperature of 1,250° C. In particular, theexamples of the present invention provided a dielectric compositionmeeting COG/CH characteristics (±30 ppm/° C., ±60 ppm/° C.) inaccordance with the EIA Standard.

On the other hand, comparative examples (1-4) out of the compositionrange of the present invention had excessively high resistivities anddid not meet COG/CH characteristics.

As apparent from the above description, the present invention provides acomposition capable of being sintered at temperature of less than 1,300°C., and even more, at a low temperature of 1,250° C., as well as beingsintered under a reducing atmosphere to be used in formation of a nickelelectrode. As a result, mismatching between a nickel electrode andceramic during the sintering process can be prevented. Further, thedielectric composition can provide a TC based electric compositionhaving a small dielectric loss and a high resistivity.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. A nonreducible dielectric composition comprising a main componentexpressed by the general formula,(Ca_(1-x)Sr_(x))_(m)(Zr_(1-y)Ti_(y))O₃, which has the ranges of 0≦x≦1,0≦y≦0.09 and 0.7≦m≦1.05; and 0.5-10 wt % of a minor component expressedby the general formula, aMnO-bSiO₂-eZrO₂(a+b+e=100), which has theranges of 20≦a≦60, 10≦b≦65 and 0≦e≦65.
 2. A multi-layered ceramiccapacitor comprising: a plurality of sheets of dielectric compositionaccording to claim 1; and a plurality of electrodes on each of theplurality of sheets, wherein the sheets and the electrodes arealternatively laminated.